Rheem RTU serial# 2M7943ADAAF351007426 what year is this??

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Rheem Product Warranty Information

1) Look for brand name of your heater on following .pdf file:
http://waterheatertimer.org/pdf/Find-Age-of-water-heater.pdf

2) Home Depot sells GE heaters made by Rheem.
I am assuming that serial number starts with 1209, and that year of manufacture is 09 for 2009.

3) These water heaters have glass vial that breaks when combustion chamber experiences overheating due to dirty combustion parts, clogged air intake, exposure to flammable vapor.
http://waterheatertimer.org/How-to-repair-Rheem-TRD.html

4) Water heater warranties are usually first-year: full parts, labor and tank. After first year: parts and tank but no labor.
Warranty may be pro-rated and the value diminishes as water heater ages.
http://waterheatertimer.org/How-to-maintain-water-heater.html

5) Warranty may not apply is customer has not followed installation and maintenance as shown in product manual, such as checking anode rod, and yearly service by trained technician.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Need new PC board probably.
And/or the required yearly general maintenance.
Unknown if this is new installation, or if parts still under warranty.
Call Rheem with serial number located on side of unit, and they can send PC board.
Copy following link for error codes and possible manual:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Rheem-CondensingTankless-maintenance-2012.pdf

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Generally the year of manufacture for Rheem is 3rd and 4th digit of serial number. 06 is 2006, 92 is 1992 etc.
Older gas water heaters are better than new ones, and easier to keep repaired and maintained.
http://waterheatertimer.org/How-to-maintain-water-heater.html
Regardless of age, the key factor is whether tank is rusted, or rusting.
Open drain valve and check if water is rusted.
http://waterheatertimer.org/Replace-anode-rod.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

the age of all water heaters is listed under the serial #, not model #. you will have to call a plumbing supply house that deals in your brand of waterheater, a.o. smith, ruud, bradfordwhite,etc.

e2 is not shown among common error codes:
Error e2 might be: Brownout condition or too low of voltage to thermostat. Double check wiring and check for 24 vac between R and C. E2 will clear 15 sec after proper voltage is restored.

Before calling service technician, open following link for Rheem troubleshoot resources including Rheem chat and typical generic manuals and common error codes:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Model number and serial number are required for Rheem contact, and then they tell you what error code means without saying how to fix it, and then tell you to call service technician.

Tankless water heater manuals each say to have qualified technician perform yearly service. Most causes for common error codes are covered by yearly service.

Yearly service is fairly standard in the HVAC and water heater industry with advancement of high-tech 'energy' saving appliances. Of course all costs are energy, and the service call probably costs more that the 'energy' saved by energy-saving appliance. But with high tech stuff like tankless, it is good to have a reliable service guy who knows your machine.
http://waterheatertimer.org/images/Tankless-wiring-1200.jpg

Check that serial number.
Rheem is first two digits= month and next two digits= year, which means 1990.
http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html

I need some upvotes for the free, hard work being done for folks.

Before calling service technician, read manual for troubleshooting and yearly maintenance requirements.
Open following links to identify same-similar product and download manual.
Once you have product showing on page, click 'specs-docs' tab to see use-and-care manual.
http://www.rheem.com/product.aspx?id=C24E3F52-A6A4-4BC7-AF5B-0DF23A7A0263
http://www.rheem.com/Products/tank_water_heaters/gas_water_heaters
http://globalimageserver.com/fetchDocument.aspx?id=c0471d58-5e59-4be6-96f7-68361b8fb515
Rheem site loads slow, and some manuals never load.
Typical power vent manual:
http://waterheatertimer.org/pdf/Rheem-power-vent-manual.pdf

I believe the 21VP is older and Rheem does not show older manuals, but manuals are generally generic enough to help greatly. Year of manufacture show as second and third digit of serial number.

Lockout condition requires service technician and part replacement, or call Rheem and have them send part.
I found one link that talks about FV lockout that may or may not pertain to your issue:
http://www.diychatroom.com/f7/rheem-hot-water-heater-pilot-burner-not-staying-lit-65755/

You can find age of water heater from serial number located on label on side of tank.
Label also shows tank size, and tank wattage and element wattage

http://waterheatertimer.org/Figure-Volts-Amps-Watts-for-water-heater.html
http://waterheatertimer.org/Water-at-bottom-of-water-heater.html

Serial number decoder:
http://waterheatertimer.org/pdf/WaterHeaterSerialNumberDecoder.pdf
For example Rheem serial number 0790...
First 2 digits are month 07 July
Next two digits are year 1990

Rheem site does not show 81v40d
http://www.rheem.com/products/tank_water_heaters/electric_water_heaters/

http://waterheating.rheem.com/dotcomWeb/pageflows/warrantyverification/WarrantyVerificationController.jpf
Just click on the above link and enter your serial number. It will give you the information you are looking for.